ui: 个人中心退出按钮提升可见度

- 顶部导航栏右侧新增退出按钮，无需滚到页面底部
- 底部退出按钮从灰色文字链接改为带边框的圆角按钮

src/app/profile/page.tsx

@@ -273,7 +273,14 @@ export default function ProfilePage() {
         >
           <ArrowLeft size={20} />
         </button>
-        <h1 className="text-base font-bold text-white">个人中心</h1>
+        <h1 className="flex-1 text-base font-bold text-white">个人中心</h1>
+        <button
+          onClick={handleLogout}
+          className="flex items-center gap-1.5 rounded-full bg-surface px-3 py-1.5 text-xs font-medium text-muted ring-1 ring-border transition-colors hover:text-rose-400 active:bg-elevated"
+        >
+          <LogOut size={13} />
+          退出
+        </button>
       </nav>
 
       <div className="mx-auto max-w-sm px-5">
@@ -666,9 +673,9 @@ export default function ProfilePage() {
         >
           <button
             onClick={handleLogout}
-            className="flex items-center gap-1.5 text-xs font-medium text-muted transition-colors hover:text-rose-400"
+            className="flex items-center justify-center gap-2 rounded-xl bg-surface px-6 py-2.5 text-sm font-medium text-rose-400/80 ring-1 ring-border transition-colors hover:bg-elevated hover:text-rose-400"
           >
-            <LogOut size={13} />
+            <LogOut size={14} />
             退出登录
           </button>
         </motion.div>